The subject invention relates to apparatus and the method of using same for therapeutic ultrasound treatment. More particularly, the subject invention is directed to an apparatus and method of using same for the therapeutic ultrasound treatment during which the transducer is maintained substantially stationary relative to the area being treated.
Ultrasound has been employed in medicine for more than 50 years. The application of ultrasound for medical treatment was introduced in Germany in the late 1930s, and in the United States in the late 1940s.
Sound with a frequency greater than 20,000 Hz is called ultrasound. For a given sound source, the higher the frequency, the less the emerging sound beam diverges. Sound at audible frequencies appears to spread out in all directions, whereas ultrasound beams are well collimated, similar to a light beam leaving a flashlight. Ultrasound beams at frequencies greater than 800 kHz are sufficiently collimated to selectively expose a limited target area for physical therapy treatment. At frequencies less than about 800 kHz the ultrasound beam""s intensity is sufficiently low as to be outside the range for physical therapy treatment, but has been used at these low intensity levels for diagnostic procedures.
Absorption of sound, and therefore attenuation, increases as the frequency increases. Absorption occurs in part because of the internal friction in tissue that needs to be overcome in the passage of sound. The higher the frequency, the more rapidly the molecules are forced to move against this friction. As the absorption increases, there is less sound energy available to propagate through the tissue. At frequencies greater than 20 MHz, superficial absorption becomes so great that less than 1 percent of the sound penetrates beyond the first centimeter.
Therefore, for physical therapy applications, the frequency range is generally considered to be limited to frequencies within the range of about 800 kHz to about 3.3 MHz. Frequently most often used for physical therapy application is a frequency of about 1.0 MHz or 3.0 MHz because they offer a good compromises between sufficiently deep penetration and adequate heating under customary exposure levels.
Sound waves can be produced as continuous wave or as pulsed wave. A pulsed wave is intermittently interrupted. Pulsed waves are further characterized by specifying the fraction of time the sound is present over one pulse period. This fraction is called the duty cycle and is calculated by dividing the pulse time on by the total time of a pulse period; e.g. time on plus time off. Duty cycles for therapy machines, when in the pulsed mode, range from about 5 per cent to about 50 percent.
The strength of an ultrasound beam is determined by its intensity. Intensity is the rate at which energy is delivered per unit area. It is expressed in units of watts per square centimeter. Intensities employed in physical therapy are limited to the range of about 0.25 to about 3.00 watts per square centimeter.
Where sound beams are pulsed, the intensity of the beam will be zero when the sound beam is off and at its maximum during the pulse. The temporal average intensity of a beam is obtained by averaging the intensity over both the on and off periods. The amount of heating depends on the temporal average intensity. The temporal average intensity is decreased proportionally to the amount of time the sound is off. Thus less heating will occur even though the temporal peak intensity is unchanged.
Because the ultrasound beam is not uniform, some regions of the beam will be more intense than other regions. The measurement of intensity gives an average intensity and is referred to as the spatial average intensity. The World Health Organization limits the spatial average intensity to a maximum of 3 watt per square centimeter. Intensities greater than 10 watt per square centimeter are used to destroy tissue surgically and intensities (temporal average) below 0.21 watt per square centimeter are used for diagnostic purposes.
Therapeutic ultrasound treatment is customarily performed using a moving transducer technique with a small layer of gel or lotion between the transducer and the tissue. This movement is to avoid damage caused by beam xe2x80x9chot spotsxe2x80x9d as is known in the industry and in general to treat areas which are typically larger than the area of the transducer.
Ultrasound treatment is an attended therapy that requires a clinician to be present to move the sound head over the treatment area. This movement of the transducer over the gel covering the treatment area causes the gel to be displaced and therefore requires constant attended application of the gel.
Movement speed rate of the transducer during treatment vary widely from one clinician to another. Therefore, there often is misuse of the treating machine, by the clinician which is caused by moving the transducer too fast, not using enough coupling medium, not moving the transducer, trying to treat too large and area, not keeping the transducer in contact with the patient and other faults.
Since treatments must be supervised by a clinician, the patient is often limited to specific treatment times with greater repetitions. It has been found that often it would be more beneficial to the patient to have fewer treatments each of longer duration.
The present invention is directed to over come one or more of the heretofore problems, as set forth above.
In one aspect of the invention, a therapeutic ultrasound system is adapted to substantially stationary transducer application during use. The system has a first means for generating a pulsed digital signal at a frequency in the range of greater than about 800 kHz to less than about 3.0 MHz and a spatial average intensity in the range of about 0.1 watt per square centimeter to about 3.0 watt per square centimeter.
A sine wave filter is connected to the first means and is adapted to receive the signal form the first means and convert it to a second signal. A programmable controlling element is connected to the sine wave filter and is adapted to deliver said second signal to a plurality of separate locations in a preselected sequence, each for a preselected period of time.
A transducer has a plurality of spaced apart piezoelectric crystals each operatively connected to the programmable controlling element for sequentially receiving the second signal and delivering a pulsed sound beam therefrom. Means is provided for maintaining the transducer substantially stationary during operation thereof.
In another aspect of the invention, a method of therapeutic ultrasound treatment is provided. A pulsed digital signal is generated at a frequency in the range of greater than about 800 kHz to less than about 3.0 MHz and a spatial average intensity in the range of about 0.1 watt per square centimeter to about 3.0 watt per square centimeter. The signal is converted to a pulsed sine wave signal. The pulsed sine wave signal is delivered to a first plurality of separate locations in a preselected sequence, each for a preselected time period. The pulsed sine wave signal is received at said first plurality of separate locations and ultrasound energy is delivered outwardly from each of said separate locations while maintaining the first plurality of separate locations substantially stationary relative to a first area being treated. Means is provided for maintaining the transducer substantially stationary during operation thereof.